The present invention is related to damper control systems, and in particular, systems and methods for controlling exhaust dampers on steelmaking furnaces.
Furnaces, including steelmaking furnaces such as electric arc furnaces for melting steel and other similar products, are typically used in combination with emission recovery systems. Emission recovery systems are needed to capture airborne particulate emissions and exhaust gases created during operation of the furnace.
The exhaust gases created in an electric arc furnace may include certain gases subject to environmental and workplace regulations. For example, gases such as carbon monoxide, sulphur dioxide, and nitrous oxides are frequently produced in the furnace. Volatile organic compounds (VOC) have also been generated during the melt process. Additionally, particulate emissions, such as slag or dust, are produced during the melting process. These exhaust gases and particulate emissions are captured and may be treated in compliance with appropriate regulations.
The volume and composition of furnace exhaust varies significantly during the melting process. The rate at which exhaust gases and particulate emissions are created depends upon many factors, such as the stage of the melting process, the temperature within the furnace, and the amount of air entering the furnace. These same factors also affect the composition of the exhaust gases as the constituent components of exhaust gases are produced or consumed within the furnace.
Another factor affecting the volume and composition of furnace exhaust is the composition of the raw materials being melted. For example, the use of scrap metal as a raw material in steelmaking has resulted in paint and other previously applied coatings, and various impurities being introduced into the furnace. During furnace operation, these impurities melt or burn further contributing to the varied nature of the furnace exhaust. Some furnaces are also equipped to inject carbon and oxygen throughout the melting process resulting in combustion that produces large volumes of gaseous reaction products that add to the exhaust gases. The gaseous reaction products are generated at a variable rate as different sources of carbon are injected into the furnace resulting in fluctuations in the volume of exhaust gases that must be evacuated from the furnace. The evacuation of exhaust gases may regulated and controlled to improve furnace operations.
Typically an emission recovery system includes an induced draft fan and one or more exhaust ducts in communication with an electric arc furnace. The induced draft fan produces a negative pressure that draws furnace exhaust into the exhaust ducts to be collected in a baghouse filter, electrostatic precipitators, or other collection system. Various configurations of exhaust ducts have been developed to improve the overall capture of exhaust gases and particulate emissions. For example, exhaust ducts have been positioned to suction exhaust directly from an opening in or adjacent the roof of the electric arc furnace. Exhaust ducts may also be configured as a canopy or hood over electric arc furnaces.
The induced draft fan causes negative pressure adjacent the fan in the exhaust duct enabling air to be drawn into the furnace, or draft. This air may be heated and combusted within the furnace and exhausted through the exhaust ducts. The exhaust gases may exceed 3000° F. upon exiting the furnace. Excessive negative pressure may cause excessive draft, and excessive draft may cause excessive amounts of air to be drawn into the furnace. Heating and/or combusting this excess air consumes energy resulting in a reduction in furnace efficiency. Further, excess air drawn into the furnace may increase the production of undesirable exhaust gases, such as nitrous oxides. This further reduces the efficiency of furnace operations and increases operating costs. Some undesirable exhaust gases may need to be scrubbed for environmental reasons. Excessive draft also causes temperature control problems and reduces efficiency, and in steelmaking affects slag foaming, slag content, skulling, and other processing parameters.
Conversely, if insufficient negative pressure is applied to the exhaust duct, not enough draft is provided and the desired portion of the exhaust gases and particulate emissions may not be drawn into the exhaust ducts, and may escape through openings in the furnace and bypass the emission recovery system. The escaping exhaust gases and particulate emissions may also cause environmental and workplace concerns. Too little draft may also cause problems related to temperature control in the furnace and excess production of potentially overheated gases. Conversely, if too much draft is applied, furnace efficiency is reduced and operating costs are increased. Thus, a balance in furnace draft control is desirable for efficient use of the furnace.
Efficient operation of a furnace therefore requires regulation of the negative pressure in the exhaust ducts and draft to the furnace. To address these problems, emission recovery systems on steelmaking furnaces have typically utilized dampers capable of adjusting the negative pressure in the exhaust ducts. Previously, exhaust dampers have been set to fixed positions during operation of the furnace. To ensure adequate capture of furnace emissions, the dampers have been set to apply a negative pressure enabling a draft capable of capturing a high volume of exhaust gases produced during operating states of the furnace. Experienced operators have manually adjusted the exhaust dampers during operation to reduce drawing excess air into the furnace. The operators would watch the furnace to detect “puffing,” or the escape of excessive exhaust gases or particulate emissions through openings in the furnace. Puffing was typically associated with flames or gases emitting from the openings in the furnace. The operator may manually adjust the damper in response to these observations. This approach required an experienced operator to monitor and adjust the exhaust damper, which may further increase the operating costs of steelmaking.
Some attempts have been made to automate damper control. For example, attempts have been made to measure the negative pressure in the furnace or exhaust ducts directly with a pressure sensor as illustrated in U.S. Pat. No. 6,301,285. In these types of systems, pressure sensors have been mounted in the electric arc furnace roof or in the exhaust duct. The pressure sensors, however, have often become clogged with dust or slag particles from the furnace exhaust. Moreover, the high temperatures within the furnace and exhaust ducts have often damaged or destroyed the sensor rendering the system inoperative and further increasing operating costs of steelmaking. Additionally, the pressure differentials that have been measured are relatively small making precise control of the dampers difficult. Typical environmental fluctuations and changes have also made pressure monitoring less reliable as the desired pressure settings may change over relatively short time periods.
Other attempts to automate emission recovery systems have relied upon measurements of the composition of furnace exhaust gases. For example, U.S. Pat. No. 6,748,004 describes a system that measures the constituents, e.g. COx, of the exhaust gas. U.S. Pat. No. 6,372,009 describes a system that measures the temperature of the exhaust gas and the amount of carbon monoxide at various points in the exhaust gas stream. Sensors in these types of systems have also been susceptible to becoming clogged or damaged by the high temperatures present in the furnace.
Accordingly, there continues to be a need for improved damper control systems that reliably capture furnace emissions while achieving improved energy efficiency and reduced operating costs.
A furnace damper control system is presently disclosed comprising    a) a furnace having at least one opening through which electromagnetic radiation from within the furnace may be sensed, an exhaust duct adapted to receive an exhaust gas stream emerging from the furnace, and a controllable damper adapted to adjust the pressure in the exhaust duct;    b) a sensor adapted to sense electromagnetic radiation emitted through one or more of the openings of the furnace and generate a sensor signal corresponding to the emitted electromagnetic radiation indicative of furnace emissions; and    c) a controller adapted to control the damper responsive to the monitoring signal indicative of the furnace emissions. The parameter of the electromagnetic radiation may be one selected from the group consisting of intensity, wavelength, amplitude, frequency, and combinations thereof.
Alternately, the furnace damper control system may comprise    a) a furnace having at least one opening through which electromagnetic radiation from within the furnace may be sensed, an exhaust duct adapted to receive an exhaust gas stream emerging from the steelmaking furnace, and a controllable damper adapted to adjust the pressure in the exhaust duct;    b) a sensor adapted to sense emitted electromagnetic radiation through one or more of the openings of the furnace and generate digital images thereof;    c) a processor adapted to process the digital images and generate a monitoring signal responsive to a parameter of the digital images indicative of furnace emissions;    d) a controller adapted to control the damper responsive to the monitoring signal indicative of the furnace emissions.
The sensor may be further capable of generating a digital image indicative of at least a part of the visible spectrum. The sensor may be a monochrome sensor or a multi-color sensor. Alternatively or in combination an infrared sensor may be employed.
The processor may be capable of comparing the intensity of pixels in the digital images to a desired reference intensity. The reference intensity may represent intensity in the visible spectrum, infrared spectrum, or both. The reference intensity may be a predetermined value or an adjustable value. The monitoring signal from the processor may correspond to a ratio of pixels of the digital images exceeding the reference intensity. Alternately or in addition, the monitoring signal may correspond to the number of pixels of the digital images having an intensity exceeding the reference intensity.
The processor may be capable of analyzing all or a part of the color spectra in the visible range of pixels of the digital images and generating a monitoring signal corresponding to the analyzed color of the pixels in the digital images. The monitoring signal may correspond to two or more parameters of pixels of the digital images to provide more accurate control.
The processor may be capable of segmenting the digital images into selected control zones, where each control zone is a portion of the digital images. The control zones may be predetermined portions of the digital images, or the control zones may be determined by the processor. The processor may be capable of processing pixels of the digital images in each control zone. In any case, the control zone may be a physical part of the digital images or selected from different parts of the electromagnetic spectrum.
The controller may comprise one selected from a group consisting of a computer, a programmable logic controller, a proportional integral derivative controller, or a combination thereof. The controller may be capable of generating a control signal corresponding to a desired adjustment of the controllable damper indicated by the monitoring signal. Alternately or in addition, the controller may be capable of comparing the monitoring signal to a set-point. In some embodiments, the controller may be capable of generating at least two control signals corresponding to desired adjustments of at least two dampers.
The furnace damper control system may include an actuator capable of positioning the damper. The actuator may be an electric motor or a pneumatic or hydraulic regulator.
The furnace damper control system may include a pressure sensor capable of generating a pressure monitoring signal.
The controller may be capable of generating a control signal corresponding to a desired adjustment of the damper indicated by the monitoring signal, the pressure monitoring signal, or combinations thereof.
Also disclosed is a method of controlling a furnace damper, the method comprising:    a) sensing electromagnetic radiation emitted through one or more openings of a furnace and generating a sensor signal corresponding to the emitted electromagnetic radiation;    b) processing the sensor signal and generating a monitoring signal responsive to a parameter of the electromagnetic radiation indicative of furnace emissions; and    c) controlling the damper responsive to the monitoring signal indicative of the furnace emissions.
Alternatively, a method of controlling a furnace damper may comprise:    a) sensing electromagnetic radiation emitted through one or more openings of a furnace and generating digital images thereof;    b) processing the digital images and generating a monitoring signal responsive to a parameter of the digital images indicative of furnace emissions; and    c) controlling the damper responsive to the monitoring signal indicative of the furnace emissions.
Also presently disclosed is a furnace comprising:    a) a converter adapted to contain molten metal;    b) an exhaust duct adapted to receive an exhaust gas stream emerging from the furnace;    c) a negative pressure apparatus adapted to draw the exhaust gas stream from the furnace through the exhaust duct;    d) a controllable damper adapted to adjust the pressure in the exhaust duct;    e) at least one opening through which electromagnetic radiation from within the furnace may be sensed;    f) a sensor adapted to sense electromagnetic radiation emitted through one or more of the openings of the furnace and generate digital images thereof;    g) a processor adapted to process the digital images and generate a monitoring signal responsive to a parameter of the digital images indicative of furnace emissions; and    h) a controller adapted to control the damper responsive to the monitoring signal indicative of the furnace emissions.
A method of making steel is also disclosed comprising:    a) charging a furnace with raw material;    b) operating the furnace to melt the steel;    c) sensing electromagnetic radiation emitted through one or more openings of the furnace and generating digital images thereof;    d) processing the digital images and generating a monitoring signal responsive to a parameter of the digital images indicative of furnace emissions; and    e) controlling the damper responsive to the monitoring signal indicative of the furnace emissions.